A typo on Gitbook guide

[riemannulus]

this one should be

.scan(String::length)
.reduce(0)...

not

.map(String::length)
.reduce(0)

here is url: https://thomasnield.gitbooks.io/rxjavafx-guide/content/2.%20RxJava%20Fundamentals.html#scan

and here is a screenshot